The invention relates to calenders and like machines in general, and more particularly to improvements in roll assemblies for use in such machines. Still more particularly, the invention relates to improvements in rolls which can be used in roll assemblies of calenders and like machines and wherein a deformable hollow cylindrical shell surrounds a fixed carrier and can be deformed by one or more hydrostatic displacing units which are installed between the carrier and the internal surface of the shell.
It is often necessary to heat the shell of a roll wherein the shell can be deformed by one or more hydrostatic displacing units. This is achieved in that a heated hydraulic fluid is supplied to the pocket or pockets of the hydrostatic bearing element or elements of the displacing unit or units and that a compressed hydraulic fluid is admitted into the plenum chamber or chambers of that bearing element or of those bearing elements which are to be moved radially outwardly away from the carrier in order to deform the adjacent portion or portions of the shell.
German patent application No. 39 09 556 of Link (published Nov. 16, 1989) discloses a roll wherein the pockets of the bearing elements in the hydrostatic displacing units receive streams of heated liquid at a constant volumetric rate. The heated liquid flows through one or more flow restrictors on its way into the pockets of the bearing elements and is maintained at a selected temperature. The pressure of heated liquid is limited due to the design of the pump which is used to force heated liquid into the pockets. A basically independent or discrete second hydraulic circuit is provided to deliver compressed liquid into the plenum chamber or chambers of one or more displacing units in order to bring about deformation of the corresponding portion or portions of the shell. The pressure of liquid which is admitted into the plenum chamber or chambers is selected by a variable-pressure pump or by a pressure regulating valve which is installed downstream of a constant-pressure pump. A bypass line branches off the conduit which delivers compressed liquid to the plenum chamber or chambers, and the outlet of the bypass line admits compressed liquid into the sump from which the pump draws a stream for liquid for introduction into the plenum chamber or chambers. A drawback of such proposal is that the plenum chamber or chambers confine stagnant bodies of compressed liquid. This can lead to overheating and decomposition of the confined liquid and results in contamination of the plenum chambers.
German patent application No. 38 13 598 of Kubik et al. (published Nov. 23, 1989) discloses a roll wherein the plenum chambers of the hydrostatic displacing units are sealed from the interior of the shell as well as from the pockets in the external surface of the respective bearing elements. This also leads to overheating of liquid in the plenum chambers.